Method and system for brake control

ABSTRACT

Methods and systems are provided to reduce a hard brake pedal feel. A brake control variable is adjusted in anticipation of a hard pedal condition to increase hydraulic brake line pressure and maintain a normal pedal feel. A pedal force is inferred from brake line pressure relative to brake booster vacuum.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/290,873, entitled “METHOD AND SYSTEM FOR BRAKE CONTROL,”filed on Nov. 7, 2011, the entire contents of which are herebyincorporated by reference for all purposes.

FIELD

The present application relates to methods and system for reducing ahard pedal condition that may occur during brake pedal operation.

BACKGROUND/SUMMARY

Braking devices for enabling vehicle speed control may be operated usingvacuum. The vacuum may be provided by the engine via the engine intakemanifold. Alternatively, a vacuum pump may be operated to provide thevacuum. As such, if there is insufficient vacuum to assist in the brakeoperation, a “hard pedal” condition may occur wherein the vehicleoperator has to provide a larger brake pedal force than expected toattain the desired braking. Various approaches have been developed tomitigate such a “hard pedal” condition.

One such approach is shown by Kamiya et al. in U.S. Pat. No. 6,754,579.Therein, an engine controller automatically starts an engine upondetermining that there is insufficient brake booster vacuum. Inparticular, Kamiya adjusts an automatic engine restart operation basedon a brake pedal depression amount and a brake booster vacuum amount.

However, the inventors herein have recognized a potential issue withsuch an approach. As one example, the operator's hard pedal feeling maybe prolonged while the engine is restarted and the appropriate amount ofvacuum is generated. As another example, there may be conditions wheneven upon restarting the engine, the desired amount of vacuum cannot begenerated due to other demands on the engine.

In one example, at least some of the above-mentioned issues may be atleast partly addressed by a method of improving a brake pedal feel,comprising: adjusting a brake control variable in response to animpending change in a pedal feel, the impending change based on ahydraulic brake line pressure relative to a brake booster pressure. Inthis way, hydraulic brake line pressure may be increased before a hardpedal condition arises.

In one example, an engine controller may infer or identify the impendingchange in pedal feel based on a hydraulic brake pressure relative to thebrake booster pressure (or vacuum level). In particular, in response toan impending change (e.g., increase) in the amount of pedal forcerequired to displace the brake pedal, the controller may infer that ahard pedal condition may arise imminently. Accordingly, before the hardpedal condition occurs, the controller may increase the hydraulic brakeline pressure by increasing an amount of hydraulic brake boost that isprovided to the brake line. Specifically, an electrically-actuatedhydraulic brake booster pump (e.g., an electric pump coupled to ahydraulic brake booster component or an ABS brake system component) maybe operated and the pump output may be increased. Alternatively, oradditionally, the vacuum level in the brake booster may be increased,for example, using vacuum from the engine intake manifold.

In this way, by increasing the hydraulic brake line pressure viaadjustments to one or more brake system components before an impendinghard pedal condition occurs, a hard pedal feel incurred by a vehicleoperator during brake application can be averted. As such, this mayimprove the operator's driving experience.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of an engine and an associated brakesystem;

FIG. 2 shows a high level flowchart of an example method for improving abrake pedal feel;

FIG. 3 shows characteristic curves of hydraulic brake line pressurerelative to brake booster vacuum that may be used to infer an impendinghard pedal condition;

FIG. 4 shows an example adjustment to one or more brake systemcomponents in response to an impending change in pedal feel.

DETAILED DESCRIPTION

The present description relates to methods and systems for improving abrake pedal feel so as to reduce the likelihood of a “hard pedal”condition in an engine system, such as the engine system of FIG. 1. Anengine controller may be configured to perform a control routine, suchas the example routine of FIG. 2, to adjust the operation of one or morebrake system components so as to increase a hydraulic brake linepressure in anticipation of an impending hard pedal condition. Thecontroller may be configured to infer an impending change in the pedalfeel (that is, the pedal force required to achieve a desired change inbrake pedal position) based on the hydraulic brake line pressurerelative to the brake boost vacuum level, for example, using thecharacteristic curves of FIG. 3. As shown in the example of FIG. 4, bymaking the appropriate adjustments before a hard pedal condition occurs,the brake line pressure may be increased so that a ratio of pedal forceapplied to brake pedal displacement can be maintained below a thresholdamount. That is, a “softer” brake pedal feel can be maintained.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 95 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from intake boostchamber 46.

Compressor 162 draws air from air intake 42 to supply boost chamber 46.Exhaust gases spin turbine 164 which is coupled to compressor 162 viashaft 161. A waste gate (not shown) coupled to the turbine may allowexhaust gases to bypass turbine 164 so that boost pressure can becontrolled under varying operating conditions.

The engine may be coupled to a brake system, such as an anti-lock brakesystem, including various brake components configured to adjust thepressure in a hydraulic brake line. These may include, for example, anelectric pump, a vacuum-actuated brake booster, and a hydraulic brakebooster, as referenced herein. Brake booster 140, including an internalvacuum reservoir, may be configured to provide a vacuum assist duringbrake application. Specifically, brake booster 140 may amplify forceprovided by foot 152 via brake pedal 150 to master cylinder 148 forapplying vehicle brakes (not shown). In one example, as depicted, thebrake booster may be coupled to the intake manifold 44 of the engine 10,downstream of compressor 162, only through a check valve 73. Herein,check valve 73 allows air to flow to intake manifold 44 from brakebooster 140 and limits air flow to brake booster 140 from intakemanifold 44. Check valve 73 accommodates fast pull down of the vacuumreservoir pressure when the reservoir pressure is relatively high andintake manifold pressure is low. Consequently, the vacuum reservoir ofbrake booster 140 is rapidly supplied with vacuum from intake manifold44 via check valve 73. In alternate embodiments, brake booster 140 mayalso be supplied with vacuum from a vacuum pump (not shown) via a checkvalve (not shown) that allows air to flow to the vacuum pump from brakebooster 140 and limits air flow to brake booster 140 from the vacuumpump.

A hydraulic brake booster 116, coupled to an electrically-actuatedhydraulic brake boost pump 117 and a hydraulic brake fluid reservoir119, may be configured to provide a hydraulic assist during brakeapplication. Hydraulic brake boost pump 117 may be electrically-actuatedand operated using a battery, for example. The hydraulic brake booster116 may be coupled between the vacuum-actuated brake booster 140 and thehydraulic brake line 111, more specifically between the brake booster140 and master cylinder 148. A braking device, such as vehicle brakescoupled to vehicle wheels (not shown), may be hydraulically coupleddownstream of master cylinder 148 via hydraulic brake line 111. Thebraking device may be any suitable device such as drum brakes, or discbrakes. Additionally, an anti-lock brake system (ABS) 113 may be coupledto the braking device, for example downstream of the master cylinder148. In one embodiment, ABS 113 may be hydraulically coupled to mastercylinder 148 and four wheel cylinders of the left front wheel, rightfront wheel, left rear wheel and right rear wheel.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing accelerator positionadjusted by foot 132; a position sensor 154 coupled to brake pedal 150for sensing brake pedal position; a knock sensor for determiningignition of end gases (not shown); a measurement of engine manifoldpressure (MAP) from pressure sensor 121 coupled to intake manifold 44; ameasurement of boost pressure from pressure sensor 122 coupled to boostchamber 46; brake booster reservoir pressure from pressure sensor 125;an engine position sensor from a Hall effect sensor 118 sensingcrankshaft 40 position; a measurement of air mass entering the enginefrom sensor 120 (e.g., a hot wire air flow meter); a hydraulic brakeline pressure from a pressure sensor (not shown) coupled to hydraulicbrake line 111; and a measurement of throttle position from sensor 58.Barometric pressure may also be sensed (sensor not shown) for processingby controller 12. In a preferred aspect of the present description,engine position sensor 118 produces a predetermined number of equallyspaced pulses every revolution of the crankshaft from which engine speed(RPM) can be determined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is described merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Now turning to FIG. 2, an example method 200 for improving brake pedalfeel is elaborated. The method includes adjusting a brake controlvariable in response to an impending change in a pedal feel, wherein theimpending change is based on a hydraulic brake line pressure relative toa brake booster pressure. By making adjustments to the hydraulic brakeline pressure, a hard pedal condition can be averted.

At 202, the method includes measuring and/or estimating engine operatingconditions. These may include, for example, engine speed, engine coolanttemperature, catalyst temperature, brake booster vacuum (that is, thevacuum level in the brake booster vacuum reservoir), hydraulic brakeline pressure, desired engine torque, vehicle speed, barometricpressure, etc. At 203, it may be confirmed that vehicle brakes have beenactuated. That is, it may be confirmed that the vehicle operator hasapplied their foot on the brake pedal and depressed the brake pedal. Assuch, in response to the brake pedal application, based on prevalentoperating conditions, the engine may continue to be fueled, or fuelingmay be discontinued. In one example, when a vehicle battery state ofcharge is lower than a threshold state of charge, the engine maycontinue to be fueled. In another example, when the vehicle batterystate of charge is higher than the threshold state of charge, adeceleration fuel shut-off operation may be performed.

Upon confirmation of brake pedal application, at 204, the methodincludes determining an impending change in brake pedal feel based onhydraulic brake line pressure relative to brake booster vacuum level. Assuch, the brake pedal feel includes a pedal force required to displacethe brake pedal to a given pedal position. Further, a normal or “soft”pedal feel may be desired wherein the pedal force required to displacethe brake pedal to the given position is maintained lower than athreshold amount. However, during certain conditions, a “hard” pedalfeel may be incurred wherein the pedal force required to displace thebrake pedal to the given position is higher than the threshold amount.As the pedal feel gets harder, a larger pedal force is needed to movethe brake pedal to the given pedal position. The controller may use alook-up table that references one or more characteristic curves, such asthose shown in FIG. 3, to determine whether an impending hard pedalcondition is present. That is, the controller may anticipate the hardpedal condition before the condition actually arises, and performmitigating actions to pre-empt the condition. As a result, the vehicleoperator may not feel a hard brake pedal during brake application.

With reference to FIG. 3, it shows at map 300, characteristic curves forchanging pedal force along the x-axis, based on a hydraulic brake linepressure (as shown along the left-most y-axis) relative to a constantbrake booster vacuum (as shown along the right-most y-axis). Herein, apedal force may be inferred based on the hydraulic brake line pressurerelative to brake booster vacuum, and without needing to estimate abrake pedal position. As such, this allows the pedal force to beinferred accurately without requiring a brake pedal position sensor,which would otherwise add to component costs. When brake operationcontinues along any of the depicted characteristic curves (that is, innormal pedal feel region 306), a normal brake pedal feel is enabled.When operating conditions cause brake operation to move to the right of,and/or below, the characteristic curves (that is, in hard pedal region308), a hard brake pedal feel is incurred. As such, when operatingconditions cause brake operation to move to the left of, and/or above,the characteristic curves (that is, in grabby pedal feel region 307), adegraded brake feel may also be incurred wherein the brakes feelextra-grabby.

As shown in map 300, for a given combination of brake booster pressurerelative to brake booster vacuum, the pedal feel changes from a softercondition to a harder condition at a given pedal force. For example, afirst characteristic curve is shown at 304 (solid line). Herein, thebrake booster vacuum may be 0.925 bar (or 27 inHg) while the hydraulicbrake line pressure is 0.9 bar. Under these conditions, a normal pedalfeel may be experienced at inferred pedal forces along the steepersection of curve 304 (as also shown by normal, or soft, pedal feelregion 306) while a hard pedal feel may be experienced when the inferredpedal force is to the right of, or below the knee region of curve 304 aswell as along the shallower section of curve 304 (as shown by hard pedalfeel region 308). As such, the knee of the curve may correspond to theintersection of the tangent of the two sections of the curve (includingthe first steeper section and the second shallower section). As thebrake booster vacuum level drops (that is, there is less vacuumavailable in the brake booster reservoir), the change in pedal feel mayoccur at relatively lower pedal forces. That is, the hard pedal feel mayoccur earlier during brake pedal application. Thus, for a secondcharacteristic curve shown at 314 (dashed line), wherein brake boostervacuum is 0.875 bar (or 24 inHg) while the hydraulic brake line pressureis 0.8 bar, the change in brake pedal feel (or knee region of curve 314)may occur at a lower inferred pedal force than for curve 304. In thisway, by comparing the estimated hydraulic brake line pressure (asestimated by a brake line pressure sensor) with the estimated brakebooster vacuum level (as estimated by a vacuum reservoir pressuresensor), a controller may determine an inferred pedal force, andaccordingly determine whether the brake pedal is in the normal pedalfeel region, or approaching the hard pedal feel region.

Returning to FIG. 2, at 206, the method includes determining whetherthere is an impending change in pedal feel, in particular, whether animpending hard pedal condition is present. As used herein, the impendingchange includes, when a change in hydraulic brake line pressure relativeto a change in brake booster pressure is higher than a threshold amount,inferring an impending hard pedal feel, and when the change in hydraulicbrake line pressure relative to the change in brake booster pressure islower than the threshold amount, inferring an impending hard pedal feelis not present, and that the brake pedal is in the normal (or soft)pedal feel region.

If an impending hard pedal condition is not confirmed, the routine mayend. Upon confirmation of the hard pedal condition, at 208, one or morebrake control variables may be adjusted before the hard pedal conditionarises to maintain a ratio of brake pedal force to brake pedaldisplacement below a threshold amount. That is, the hard pedal feel maybe pre-empted by maintaining the soft pedal feel using adjustments toone or more brake system components.

In one example, as shown at 210, the brake control variable includes ahydraulic brake boost from a hydraulic brake booster of the vehicle'sbrake system. Herein, the adjustment may include, as the impendingchange in pedal feel moves towards a harder pedal feel, increasing thehydraulic brake boost supplied to a hydraulic brake line to increase thehydraulic brake line pressure. Specifically, increasing the hydraulicbrake boost may include operating an electrically-actuated hydraulicbrake boost pump to increase a hydraulic pressure (or flow) output fromthe pump. The pump may be coupled to other brake system components, suchas anti-lock brakes.

In another example, as shown at 212, the brake control variable mayinclude a brake booster vacuum. Herein, the adjustment may include, asthe impending change in pedal feel moves towards a harder pedal feel,increasing the brake booster vacuum by operating the engine for aduration. For example, if the engine was in a DFSO condition when theimpending change in pedal feel is confirmed, the engine may be refueledand spun for a duration to generate intake manifold vacuum that is thenused to refill the vacuum reservoir of the vacuum-actuated brakebooster.

In still further examples, as elaborated below with reference to theexample of FIG. 4, a combination of hydraulic brake boost and vacuumgeneration may be used to increase the hydraulic brake line pressure andreduce the likelihood of a hard pedal condition. In this way, byinferring an impending hard pedal condition before the hard pedalcondition actually occurs, and by also performing adjustments to brakesystem components before the hard pedal condition occurs, hard pedalconditions may be reduced and driver pedal feel may be improved.

Now turning to FIG. 4, map 400 shows an example scenario whereinadjustments to one or more brake system components (or brake controlvariables) are used to improve a brake pedal feel. Map 400 depictsexample changes in a brake pedal position at graph 402, changes in aratio of pedal force to brake pedal displacement (herein also referredto as the pedal feel) are depicted at graph 404, changes to a brakebooster vacuum level are depicted at graph 406, changes in a hydraulicbrake booster pump output are depicted at graph 408, changes in ahydraulic brake boost pressure are depicted at graph 410, and changes ina hydraulic brake line pressure are depicted at graph 412, over aduration of vehicle operation (along the x-axis).

At t0, the vehicle operator may initiate a brake pedal application (asindicated by a change in brake pedal position or displacement). As such,the operator may continue pressing down on the brake pedal between t0and t4, and may then maintain the pedal position between t4 and t4. Theoperator may then release the brake pedal at t5 (graph 402). As such, atthe time that the operator initiates brake pedal application, the brakebooster vacuum may be higher than a threshold amount such that the brakebooster is able to provide sufficient vacuum brake assist and such thatthe change in pedal force to pedal displacement (graph 404), that is thepedal feel, remains “soft” or normal (that is, lower than a thresholdamount). At t1, based on the combination of hydraulic brake linepressure relative to the brake booster vacuum level, in the absence ofany further adjustments, the pedal force required to displace the brakepedal may start to increase (see dashed line 405) such that an eventualhard pedal condition may occur. For example, in the absence of anadjustment, the pedal force to pedal displacement ratio may start toincrease until an actual hard pedal condition is incurred at t4. As thebrake pedal is depressed, and a vacuum assist is provided, the hydraulicbrake pressure may start to increase (graph 412). However, in theabsence of any further adjustments, after t1 it may also not be possibleto continue raising the hydraulic brake line pressure responsive to thecontinued change in brake pedal position. That is, hydraulic brake linepressure may saturate (as shown at dashed line 413).

Accordingly, at t1, a controller may infer an impending hard pedalcondition, before the hard pedal condition actually occurs, based on thebrake booster vacuum relative to the hydraulic brake line pressure.Specifically, the hard pedal condition is not inferred based on anestimated change in brake pedal position. In response to the inference,between t1 and t4, the controller may be configured to increase thehydraulic brake line pressure via adjustments to one or more brakesystem components to maintain a ratio of pedal force to brake pedaldisplacement at less than a threshold amount (that is, to maintain thepedal feel on solid line 404). As such, the adjustments to the one ormore brake system components may be performed before the hard pedalcondition occurs.

In the depicted example, the one or more brake system components includean electrically-actuated hydraulic brake booster pump and avacuum-actuated brake booster. In the depicted example, the controllermay first perform adjustments to the hydraulic brake booster pump andthen, if needed, may further perform adjustments to the brake boostervacuum. Specifically, between t1 and t2, the controller may operate theelectrically-actuated pump to increase pump output (graph 408) andcorrespondingly increase a hydraulic brake boost pressure (graph 410)provided to the hydraulic brake line. As such, this allows the hydraulicbrake line pressure to continue increasing responsive to the continuedbrake pedal displacement (graph 412).

In one example, based on the state of charge of the battery that powersthat electric pump, the pump may be operated at the maximum output for aduration corresponding to t2 through t3, after which operation of thepump may need to be discontinued. As such, if pump operation isdiscontinued while the brake pedal continues to be applied, the changein pedal feel to a harder feel may return. Accordingly, in anticipationof no further pump output being available after t3, the controller mayinitiate adjustments to the brake booster vacuum. In one example, a DFSOoperation may have been initiated in response to the brake pedalapplication at t1. Accordingly, at t2, the controller may return fuel tothe engine and operate the engine for a duration (between t2 and t4) toincrease intake manifold vacuum, and accordingly increase the brakebooster vacuum. In particular, between t2 and t3, while the pump outputand the corresponding hydraulic brake boost is available, brake boostervacuum may be increased at a first, smaller rate. Then, between t3 andt4, when the pump operation is discontinued and the hydraulic brakeboost is not available, but the brake pedal continues to be applied,brake booster vacuum may be increased at a second, higher rate tocompensate for the (now unavailable) hydraulic brake boost assist whilealso providing the required vacuum assist for the brake pedalapplication. In this way, the example depicts includes increasinghydraulic brake line pressure up to a first threshold pressure (that is,the brake line pressure attained at t2) by increasing hydraulic brakeboost pressure, and then further increasing hydraulic brake linepressure beyond the first threshold pressure by increasing brake boostervacuum.

Between t4 and t5, while pedal position is maintained, brake boostervacuum and hydraulic brake line pressure may be maintained. Then at t5,in response to the brake pedal being released, the brake line pressureand the brake booster vacuum may be reduced.

In this way, by increasing a hydraulic brake line pressure viaadjustments to one or more brake system components, the pedal force topedal displacement ratio for a brake pedal may be maintained within athreshold amount. By performing the adjustments in response to animpending change in a pedal feel, a hard pedal condition can be averted.By inferring the impending a hard pedal condition based on hydraulicbrake line pressure and brake booster vacuum, the need for expensivebrake pedal position sensors for detecting a hard pedal condition can bereduced. By identifying an impending hard pedal condition, andmitigating the impending hard pedal condition before the conditionactually occurs, a vehicle operator's drive experience can be improved.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for improving brake pedal feel, comprising: inferring animpending hard pedal condition, before the hard pedal condition occurs,based on a brake booster vacuum relative to a hydraulic brake linepressure; and in response to the inference, increasing the hydraulicbrake line pressure before the hard pedal condition arises viaadjustments to a brake system component to maintain a ratio of pedalforce to brake pedal displacement at less than a threshold.
 2. Themethod of claim 1 wherein a vacuum level in the brake booster may isincreased using vacuum from an engine intake manifold.
 3. The method ofclaim 2 wherein the engine is turbocharged.
 4. The method of claim 3,wherein the adjustments to the one or more brake system components areperformed before the hard pedal condition occurs.
 5. The method of claim3, wherein the one or more brake system components include anelectrically-actuated hydraulic brake booster pump, and avacuum-actuated brake booster.
 6. The method of claim 5, wherein theadjustments include operating the electrically-actuated pump to increasea hydraulic brake boost pressure.
 7. The method of claim 5, wherein theadjustments include operating an engine for a duration to increase thebrake booster vacuum.
 8. The method of claim 3, wherein the hard pedalcondition includes requiring a larger pedal force for a given brakepedal displacement.
 9. The method of claim 3, wherein the hard pedalcondition is not inferred based on an estimated change in brake pedalposition.
 10. A method for improving brake pedal feel in a vehicle withan engine, comprising: boosting engine intake air via a compressor; andupon brake pedal application, adjusting a brake control variable inresponse to an impending change in a pedal feel towards a harder pedalfeel, the impending change inferred based on a hydraulic brake linepressure relative to a brake booster pressure before the harder pedalfeel occurs.
 11. The method of claim 10 wherein the compressor iscoupled through a shaft to a turbine, the turbine having a wastegate.12. The method of claim 11, wherein the adjustment is performed beforethe harder pedal feel changes, the adjustment maintaining the pedal feelby maintaining a ratio of pedal force to brake pedal displacement atless than a threshold.
 13. The method of claim 12, wherein the impendingchange in pedal feel is inferred without estimating a brake pedalposition.
 14. The method of claim 12, wherein the impending change inpedal feel includes, when a change in hydraulic brake line pressurerelative to a change in brake booster pressure is higher than athreshold amount, inferring an impending hard pedal feel.
 15. The methodof claim 12, wherein the brake control variable includes a hydraulicbrake boost pressure, and wherein the adjustment includes, as theimpending change in pedal feel moves towards the harder pedal feel,increasing the hydraulic brake boost pressure to increase the hydraulicbrake line pressure by increasing output of an electrically-actuatedhydraulic brake booster pump.
 16. The method of claim 15, wherein thepedal feel includes a pedal force required to displace a brake pedal toa given pedal position, and wherein the harder pedal feel includes apedal force greater than a threshold amount to move the brake pedal tothe given pedal position.
 17. The method of claim 15, wherein increasingthe hydraulic brake boost pressure includes operating theelectrically-actuated hydraulic brake booster pump to increase a pumpoutput, the pump coupled to a brake system of the vehicle.
 18. Themethod of claim 12, wherein the brake control variable is a brakebooster vacuum.
 19. The method of claim 18, wherein the adjustmentincludes, as the impending change in pedal feel moves towards the harderpedal feel, increasing the brake booster vacuum by operating the enginefor a duration.
 20. The method of claim 10 wherein the engine includesdirect fuel injection.